The present invention relates to a method of coating a support with a thermoplastic resin film.
A method of coating a substrate with a resin by heat-melting a thermoplastic resin (referred to as "resin", simply hereinafter) such as polyolefin to extrude the melted resin in a film state on a substrate such as paper through an extruder, and by pressing the extruded resin on the substrate by means a nip roll or the like is called extrusion coating (also referred to as "extrusion laminating"), which has been widely adapted in manufacturing photographic resin-coated paper or wrapping paper (for instance, Japanese Patent Kokai-Publication No. 50-155222).
However, with increasing utility of the extrusion coated products (laminate products), diversified requirements for the product quality have arisen. As a result, there occur cases where ordinary extrusion coating devices cannot satisfy these various requirements. In particular, in the case of resin coated paper used as a support (or substrate) for photographic printing paper, there has arisen a problem in that the conventional extrusion coating device cannot cope with the above-mentioned problem since high quality is required.
In the paper as the support for photographic printing paper which is extrusion coated by the prior-art extrusion coating device, there exists a problem in that a great number of craters are produced. The so-called craters are formed as concave recesses on the coated film resin side due to air entrained by the cooling rolls and enclosed between the resin film and the cooling roll.
When the number of craters increases outer appearance of the products is damaged and therefore the quality is degraded, and further, the value of products is damaged in the case of the paper as the support for photographic printing paper because the surface luster is lowered.
Further, with an increasing production speed, the number of craters increases. Therefore, in the case of the paper as the support for photographic printing paper, it has been difficult to increase the production speed and therefore the productivity.